/Fx (Merge Injected Code)


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The latest version of this topic can be found at -Fx (Merge Injected Code).

Produces a copy of each source file with injected code merged into the source.


To distinguish a merged source file from an original source file, /Fx adds an .mrg extension between the file name and file extension. For example, a file named MyCode.cpp containing attributed code and built with /Fx creates a file named MyCode.mrg.cpp containing the following code:

//+++ Start Injected Code  
[no_injected_text(true)];      // Suppress injected text, it has   
                               // already been injected  
#pragma warning(disable: 4543) // Suppress warnings about skipping   
                               // injected text  
#pragma warning(disable: 4199) // Suppress warnings from attribute   
                               // providers  
//--- End Injected Code  

In an .mrg file, code that was injected because of an attribute will be delimited as follows:

//+++ Start Injected Code  
//--- End Injected Code  

The no_injected_text attribute is embedded in an .mrg file, which allows for the compilation of the .mrg file without text being reinjected.

You should be aware that the .mrg source file is intended to be a representation of the source code injected by the compiler. The .mrg file may not compile or run exactly as the original source file.

Macros are not expanded in the .mrg file.

If your program includes a header file that uses injected code, /Fx generates an .mrg.h file for that header. /Fx does not merge include files that do not use injected code.

To set this compiler option in the Visual Studio development environment

  1. Open the project's Property Pages dialog box. For details, see How to: Open Project Property Pages.

  2. Click the C/C++ folder.

  3. Click the Output Files property page.

  4. Modify the Expand Attributed Source property.

To set this compiler option programmatically

Output-File (/F) Options
Compiler Options
Setting Compiler Options